For a service call in Streamwood we bring torsion springs sized for a standard 16-foot steel sectional door, since that's what most of the town's garages were built with. That means stocking the common wire gauges for a single torsion shaft rather than the older double-shaft, side-mounted spring setups you'd need for pre-1970s construction. We also carry galvanized lift cables, drums, and end bearings - the parts that wear out on the same schedule as the spring because they share the load. Rollers get replaced in sets, not one at a time, since a mismatched set just shifts the wear to whichever roller is newest. What we don't carry on the truck is custom millwork for wood carriage-style doors; those aren't common in this housing stock and if we run into one, it's a special order, not a same-visit part.